1. Field of the Invention
This invention relates in general to the field of control devices for the operation of oilfield closing devices such as blowout preventers, diverters, valves and the like. In particular, the invention relates to control systems for the emergency operation of blowout preventers.
2. Description of the Prior Art
Prior art control systems for the operation of blowout preventers such as annular blowout preventers, ram blowout preventers, diverters and the like, have included a source of hydraulic power and a control valve system for directing closing or operating hydraulic pressure to the closing device for an oil and gas well. In general, the source of hydraulic power includes accummulator bottles and hydraulic pumps.
Accumulator bottles are containers which store hydraulic fluid under pressure for use in effecting blowout preventer closure. Through the use of compressed nitrogen gas, these containers store energy which can be used to effect rapid blowout preventer closure. The prior art systems have required that all blowout preventer closing units should be equipped with accummulator bottles with sufficient volumetric capacity to provide the usable hydraulic fluid volume (with the pumps inoperative) to close one pipe ram and an annular preventer in a blowout preventer stack plus the volume to open a hydraulic choke line valve. In general, the accummulators are called upon to be able to close each ram preventer within thirty seconds. Closing time is generally required to not exceed thirty seconds for annular preventers which are smaller than twenty inches and forty-five seconds for annular preventers which are twenty inches in diameter and greater. Thus, the accummulators are called upon to close the annular and ram blowout preventers in an emergency situation, such as a well kick.
In general, the control system for a blowout preventer stack also requires a pump system. A general requirement is that if the accummulator system were to be removed from service, the pumps should be capable of closing the annular preventer on the size drill pipe being used plus opening the hydraulically operated choke line valve and obtain a minimum of two hundred psi pressure above accummulator precharge pressure on the closing unit manifold within two minutes or less.
In general, the power for closing unit pumps should be available to the accummulator unit at all times such that the pumps will automatically start when the closing unit manifold pressure has decreased to less than ninety percent of the accummulator operating pressure. Two or three independent sources of power are generally required on each closing unit. The dual source power system usually recommended is an air system plus an electrical system.
The source of hydraulic power passes through regulators and control valves before being applied to the individual annular or ram blowout preventers.
The prior art control systems as described above, although reliably are not infallible. Pumps will not operate when their usual power sources are interrupted. It is conceivable that the electric pump and an air pump may simultaneously fail. Accummulators do not function properly at times due to loss of gas precharge, due to closed block valves or due to operator failure to operate a proper manifold valve. In addition, regulators and fluid control valves of the control panel may at times be inoperative or fail.